The subject matter disclosed herein relates to casting methods, and more particularly to casting methods which provide targeted reinforcement to molded articles provided therefrom by improving at least one physical property.
Casting is a process for shaping a material into a solid article. Casting provides an efficient and economical commercial manufacturing process for producing molded articles having desired and/or complex shapes. In the casting process, a liquid material is poured or introduced into a mold containing a hollow cavity of the desired shape where the liquid material solidifies upon cooling. The newly formed solid is referred to as a “casting.” Once solidified, the casting is removed from the mold.
In metal casting, the liquid material is a molten or liquid metal material. Metal casting is used to produce a number of components used in gas turbine engines. One approach to casting gas turbine engine components is to cast multiple components, such as a turbine blade and a squealer tip of a gas turbine engine bucket, in a single metal casting using a single metal casting material. Such an approach allows for multiple components to be cast as a single integral piece, rather than separate components to be joined together by welding, brazing or other methods. Casting multiple components as a single casting also reduces processing costs by reducing the total number of casting procedures used to produce the components.
Metal castings which are used as gas turbine engine components are subjected to various physical stresses during the operation of the gas turbine engine. Gas turbine engine components which are subjected to high temperatures, rubbing, e.g., between the squealer tip of a turbine blade and a housing, or rotary motion suffer from wear, fatigue, reduced tensile strength and/or creep stress, resulting in cracking and material loss. These physical stresses detrimentally affect the performance of the gas turbine engine component, leading to an increase in repairs, an increase in the frequency of routine service interval periods, and a decrease in the overall lifetime of use of the gas turbine engine component before the component is replaced. Such repairs, routine maintenance and replacement represent a substantial economic cost.
Particular regions of gas engine turbine components which have undergone cracking and/or material loss due to these physical stresses are re-built using welding or brazing methods. One drawback associated with the use of welding or brazing methods to repair damaged regions of gas turbine engine components is that the welding or brazing material used to re-build the damaged region has poor oxidation resistance due to the weldability properties of the welding or brazing material. Consequently, the degree to which the welding or brazing repair extends the lifetime of the component is limited by the poor oxidation resistance of the welding or brazing material.
Therefore, a need exists for a method of casting which provides targeted reinforcement to molded articles in order to improve at least one physical property, such as oxidation resistance, wear resistance, fatigue resistance, creep strength, tensile strength and high temperature resistance, or a combination comprising at least one of the foregoing, and/or to improve weld fabrication properties, thereby extending the period of time between repairs, routine service intervals and/or the lifetime of the gas turbine component.